With the rapid development of industry and commerce, a large population migrates to cities. In order to meet the inhabitation need, the buildings in city are prompted to be higher and higher. Since the stories of buildings are inevitably increasing, elevators have become the essential installations of high buildings for the convenience of the users in the buildings.
Since elevators have become the essential installations for shuttling between stories, the utility rate has reached a high position. Furthermore, with the increase of building height as well as the close relation between the safety of elevators and the safety of individuals, the safety of elevators has become even more important.